Chemistry 143 Empirical Formulas Dr. Caddell. Synthesis of Zinc Iodide and Magnesium Oxide

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1 Synthesis of Zinc Iodide and Magnesium Oxide In this lab you will synthesize zinc iodide from zinc metal and solid iodine. You will also synthesize magnesium oxide from magnesium metal and oxygen. Equipment You will need one 150 ml beaker, a 600 ml beaker (your waste beaker), crucible tongs, a Bunsen burner, an iron ring, a ring stand, a clay triangle, a (dirty) crucible and crucible cover, crucible tongs, and wire gauze. Chemicals You will need about 1.2 g of zinc and about 1.2 grams of iodine, about 20 ml of 0.2 M acetic acid,about 10 ml of acetone, and about 0.5 grams of magnesium ribbon. CAUTION! IODINE IS TOXIC! BE CAREFUL TO NOT GET IT ON YOUR SKIN! CAUTION! ACETONE IS FLAMMABLE! DO NOT GET IT NEAR ANY FLAMES OR HEAT! Introduction In this experiment we will study the combination reaction between zinc metal and iodine, as well as the combination reaction between magnesium and oxygen. The expected reactions are given by the balanced chemical equations: (Equation 1a) (Equation 1b) You will synthesize zinc iodide and calculate your experimental formula. This may or may not be ZnI 2. If it is not, the reason is that there was some experimental error. You will synthesize magnesium oxide by combusting magnesium metal in air. The air provides the oxygen needed. However, since air is about 78% nitrogen, another combination reaction also occurs: (Equation 2) In order to be able to calculate your experimental empirical formula for magnesium oxide you need to make sure that all of the magnesium reacts with oxygen. So we react the magnesium nitride with water forming magnesium hydroxide, magnesium oxide,and ammonia gas: 1 of 5

2 (Equation 3) We convert all of the magnesium hydroxide to magnesium oxide by heating it: (Equation 4) Procedure PART A: ZINC IODIDE 1.) Weigh your 150 ml beaker, recording the mass to 3 places past the decimal. (A1) 2.) With the beaker still on the balance tare the balance. Remove the beaker from the balance, making sure the balance remains tared. 3.) Place about 1.2 grams of zinc into the beaker and place it back on the balance. Record the mass of zinc to 3 places past the decimal. (A2) 4.) Tare the balance again and remove the beaker from the balance, making sure the balance remains tared. 5.) Add about 1.2 grams of iodine to the beaker and place it back on the balance. Record the mass of iodine to 3 places past the decimal. (A3) 6.) Add about 5 ml of 0.2 M acetic acid to the zinc and iodine in the beaker. 7.) Swirl the beaker occasionally. The reaction is complete when the solution is colorless. To make sure of this, put the beaker on a piece of white paper, or hold a piece of white paper behind the beaker. Even a faint tinge of yellow means the reaction is not complete. 8.) While waiting for the reaction to go to completion start the magnesium oxide portion of this experiment. 9.) Once the reaction is complete all of the iodine will have reacted. The solution will contain aqueous zinc iodide and acetic acid. There will be excess zinc in the beaker. 2 of 5

3 Decant the solution into your waste beaker. Make sure that all of the excess zinc metal remains in the original beaker. Some of the solution will remain with the zinc, it is more important to keep all of the zinc in the beaker than it is to get all of the solution out. 10.) Add about 3 ml of 0.2 M acetic acid to the beaker with the solid zinc. Swirl it a few times, then decant most of the solution into your waste beaker, making sure to leave all of the solid zinc in the original beaker. This is called washing the zinc. 11.) Wash the zinc 2 more times with the acetic acid (for a total of 3 washings), decanting the solution into your waste beaker. 12.) Wash the solid zinc 3 times with D.I. water, decanting the D.I. water into your waste beaker. 13.) Empty your waste beaker (down the drain). 14.) Add about 3 ml of acetone to the beaker with the solid zinc. Swirl it a few times, then decant most of the solution into a dry beaker, making sure to leave all of the solid zinc in the original beaker. DO THIS IN THE HOOD! 15.) Wash the zinc 2 more times with the acetone (for a total of 3 washings), decanting the solution into your waste beaker. DO THIS IN THE HOOD! 16.) Mark the beaker containing zinc with the word Zinc using a Sharpie (make sure not to write on the white part) and place it in your locker until next week. 17.) Weigh the beaker with the zinc in it when you come to lab next time. Record the mass to 3 places past the decimal. (A4) 3 of 5

4 PART B: MAGNESIUM OXIDE 1.) Weigh a clean, dry crucible with it s cover. Record the mass to three places past the decimal. (B1) 2.) Weigh about 0.3 grams of magnesium ribbon directly on the balance (make sure it is zeroed first) and record the mass to three places past the decimal. (B2) 3.) Place the magnesium ribbon inside of the crucible and put the lid on slightly ajar. 4.) Place the crucible, cover, and magnesium in the clay triangle in the iron ring on the ring stand. 5.) Heat the crucible with the Bunsen burner strongly for 20 minutes. The crucible should glow red. 6.) After 20 minutes turn off the Bunsen burner and place your crucible and cover on your wire gauze using the crucible tongs. 7.) After the crucible is cool to the touch, add about 3 ml of D.I. water to the crucible and place it back in the clay clay triangle in the iron ring above the Bunsen burner. 8.) Heat the crucible gently for 5 minutes and then strongly (the crucible should glow red) for another 10 minutes. 9.) Turn off the Bunsen burner and place the crucible and cover on your wire gauze using your crucible tongs. 10.) When the crucible is cool enough to pick it up by hand weigh the crucible, cover, and magnesium oxide on the balance. Record the mass to three places past the decimal. (B3) 11.) Empty your crucible into the garbage and clean it out. 4 of 5

5 DATA Mass of 150 ml beaker (A1) Original mass of zinc (A2) Mass of iodine (A3) Mass of beaker+zinc after drying (A4) Mass of crucible and cover (B1) Mass of magnesium ribbon (B2) Mass of crucible, cover, and magnesium oxide (B3) 5 of 5